GB2165910A

GB2165910A - Pipe coupling protection

Info

Publication number: GB2165910A
Application number: GB08524968A
Authority: GB
Inventors: Jan Orbeck Berg
Original assignee: VIKING MJONDALEN AS
Current assignee: VIKING MJONDALEN AS
Priority date: 1984-10-22
Filing date: 1985-10-10
Publication date: 1986-04-23
Also published as: DK462385A; NO844213L; DE3537427A1; SE8504979L; GB8524968D0; NL8502879A; DK462385D0; SE8504979D0

Abstract

A corrosion protected pipeline eg a subsea oil or gas pipeline, comprises a metal pipe (1, 1A) having a corrosion protective coating (2) and outside this an insulting layer (3) as well as an outer sheath (4, 4A) which preferable consists of rubber. Lengths of metal pipe (1, 1A) are welded (10) together after which each joint portion is corrosion protected and insulated, for example with PVC foam (13). On the outer sheath (4) adjacent the end of the metal pipe (1) there is provided a rubber sleeve (5) under radial prestressing. After welding of the metal pipe (1) to an adjacent pipe (1A) and application of a corrosion protective layer (12) and an insulating layer (13) on the joint portion, the rubber sleeve (5) is displaced longitudinally by means of a tool (20) eg a vacuum head over the joint portion and under radial elastic contraction is allowed to clamp tightly around the joint portion. <IMAGE>

Description

SPECIFICATION Method of joining corrosion protected pipelines and pipe section for use when carrying out the method This invention relates to the joining of pipelines of the type which is provided with heat insulation and corrosion protection. Such pipelines comprise sections or lengths of metal pipe having a corrosion protective coating and outside this an insulating layer as well as an outer sheath. In many uses an outer sheath of rubber is preferred. When constructing a pipeline sections of these metal pipes are welded together and then each joint portion is corrosion protected and insulated, for example with PVC foam. In some cases heat insulation may be unnecessary.

Pipelines of this type may have various uses, and a particularly interesting use in this connection is for subsea oil pipelines, in which heat insulation is desired and strict requirements are imposed with respect to corrosion protection and the coating of the pipeline, inter alia so as to withstand mechanical stresses during laying and operation.

The potentially weak points at such a pipeline are just the joint portions at which in addition to the actual welding operation there must be provided for insulation and corrosion protection which at least should be equivalent to what is obtained along the remaining length of each pipe section, as this is being manufactured at a manufacturing plant. When a subsea pipeline is laid from a laying vessel the joining will have to be effected in very short time, which involves additional strict requirements to the joining method. There is here the question of an available time for each joint of a few minutes, after which the individual pipe sections with joint portions are successively fed into the water in order to be laid on the bottom. Such pipelines may be used at depths as much as about 200 meters for the transport of oil and/or gas on the sea bottom.

The actual laying or feeding-down as mentioned also leads to rather high stresses at the pipe joints just completed.

Examples of the design of such insulated pipelines may be found inter alia in Published French Patent Application No. 8 221 175 and Norwegian Patent Application No. 83.4757.

None of these, however, show any satisfactory solution to the specific joining problems being discussed above.

Thus, it is an object of this invention to provide a method of joining pipelines of the type stated above, aiming at a reliable protection against corrosion and other stresses at the same time as the joining may be effected within comparatively short time at the working site concerned, which may be either at a laying vessel at sea or when similar pipelines are constructed on land.

The novel and specific features of the method according to the invention appear from the claims. The invention also comprises the particular embodiment of the individual pipe sections or metal pipes being used in connection with the method, for joining these together into pipelines having a larger or smaller length, which may be from a few hundred meters up to hundreds of kilometers.

The advantages obtained by means of the invention primarily consist therein that the joining may be carried out quickly, and that the pipe joints will have a reliable corrosion protection, insulation and mechanical sheathing which resist the various stresses to which such pipelines are subjected, both during construction or laying and during the lifetime of the pipeline under varying operational conditions. Moreover, at the joint portions there is used the same or similar materials as along the remaining pipe section length, so that there is provided a unitary and continuous or through-going structure in which an outer rubber sleeve constitutes a strong outer protection which is equivalent to the outer sheath on the main part of each pipe section. This outer sheath is suitably made of polychloroprene rubber, similar to the rubber sleeve.The thickness of the sleeve preferably is the same as the thickness of the sheath, for example 1015 mm for subsea oil pipelines of interest.

In the following description the invention shall be explained more closely with reference to the drawings, in which: Fig. 1 shows an example of the design at the end of a pipe section,prepared for joining according to this invention, Fig. 2 shows a partially completed pipe joint, Fig. 3 shows in cross-section insulation elements which may be used in the pipe joint and Fig. 4 shows in an enlarged longitudinal section, closer details at a pipe joint made according to this invention.

In Fig. 1 there is shown a metal pipe, preferably a steel pipe 1, which from a manufacturing plant has been provided with an inner corrosion protective layer 2 which for example may consist of polychloroprene rubber, and outside this an insulating layer 3 which as known per se, may consist of PVC foam with closed cells, for example cup shaped elements, an outer rubber sheath 4 which sealingly encloses the insulating layer. As mentioned in the introductory part of this description various pipe designs of this kind are previously known, and there may be utilized various types of materials and manufacturing methods for the corrosion protection and the insulation of the pipes. There will inter alia as a rule be practical to sandblast the steel pipe first and possibly apply a primer thereon before applying the coating 2.

With the design of the end portion of the pipe as shown in Fig. 1, this is prepared for being joined to the end of a corresponding pipe by welding. Thus, the end of pipe 1 is chamfered for a wedge shaped welding seam.

Furthermore, Fig. 1 shows a sleeve 5 mounted outside the sheath 4 adjacent the end portion of the pipe section. The sleeve 5 is made of rubber, possibly the same rubber material as in the sheath 4, and is mounted outside the latter in such a manner that the sleeve is clamped around the sheath with a predetermined prestressing force. The mounting of the sleeve 5 outside sheath 4 may for example take place by means of a suitable tongue-like tool which first expands the sleeve 5 and then passes this over the pipe end with sheath 4 and locates the sleeve at the place shown. It may be an advantage that this rubber sleeve is manufactured by molding so that it will have high quality properties with respect to mechanical strength, life-time and the like.

The degree of prestressing may vary depending upon the different dimensions being involved in the pipeline design, including the structure of the joint itself. It is obvious, however, that the rubber material employed in the sleeve 5 makes possible a large range of prestressing degrees, so that at this point there is a great freedom of choice in the design. In certain cases a prestressing degree of about 15 % may be suitable.

Fig. 2 shows two end portions of pipe sections during joining. A steel pipe 1 is welded to a steel pipe 1A by a weld 10 in a conventional manner. Steel pipe 1A has corrosion protection and insulation applied in a way corresponding to what is described with respect to pipe 1 with reference to Fig. 1. After welding and possible brushing and priming there is applied a corrosion protective layer 12 at the joint portion shown, which comprises the short end portions of each of the pipes 1 and 1A. Layer 12 may consist of a material known per se, for example rubber which may be applied by means of known methods. It is a big advantage when the layer 12 consists of a material being self-curing at the temperatures which will exist during the construction of the pipeline, possibly also during the subsequent operation thereof.For example there are found self-curing rubber compositions which are very suitable for this layer. The thickness of the layer may be 5-6 mm possibly more or less depending upon the field of use.

Outside the layer 12 there are mounted two insulation elements or cups the cross-section of which is shown at an enlarged scale in Fig.

3. In practice the exterior and the interior of the insulation cups 13 may be provided with a sealing agent, for example urethane or the like. As shown in Fig. 3 the insulation cups may have a groove and a tongue 14, 15 for easy and secure assembly. It appears from the cross-section in Fig. 3 that the insulation in the form of PVC foam lies in two layers 13A, 13B having an intermediate rubber layer and besides similar rubber layers inside and outside. These rubber layers are designated 13C in Fig. 3. It is an advantage that the outer rubber layer extends somewhat beyond the edge of the PVC cups along one longitudinal edge, with a corresponding uncovered edge portion at the opposite side, so that in the assembled insulation there will be an exterior overlap with this outer rubber layer.

Considering again Fig. 2 there will be seen a tool 20 in the form of a vacuum head which by a conduit 21 may be connected to a source of vacuum with a pump and a vacuum tank. As shown the vacuum head 20 is applied around the rubber sleeve 5 and upon application of vacuum through the hose 21, is adapted to exert a suctional effect on the outer surface of the sleeve 5 so that this will be subjected to an expansion and thereby will be disengaged from the surface of the sheath 4. In order to loosen the sleeve 5 in this manner it is an advantage that the vacuum effect is applied with an initial shock-like pressure reduction.

With the expanded sleeve 5 kept in the vacuum head 20 this is moved in the longitudinal direction of the pipeline towards the right in Fig. 2, so that the sleeve is displaced inwardly over the joint portion and the insulating layer 13 which has been applied thereto beforehand. The length of sleeve 5 corresponds to the mutual distance between the cutting surfaces of the rubber sheath on the respective pipe ends. When the vacuum head 20 has brought the sleeve 5 into a correct position, the vacuum effect is released by means of a suitable valve or the like, and the rubber sleeve 5 as a result of the prestressing thereof, will snap tightly around the insulating layer 13.

The manner of assembly described here is not the only possible one, since the mounting may also take place without the use of vacuum. An alternative method consists therein that by means of a suitable tool there is injected a lubricant between the sheath 4 and the sleeve 5 prior to the necessary displacing movement. A suitable lubricant, for example polyurethane, will lead to a substantial reduction of the friction between sheath and sleeve, so that the movement may take place by means of a clamp or the like which acts against that end of the sleeve which is most remote from the joint portion. As another alternative to the loosening of the sleeve and making possible the displacing movement thereof, compressed air may be supplied between the sheath and the sleeve before and during displacement. The use of compressed air may possibly be in combination with the use of a lubricant as mentioned above.

Irrespective of the manner of bringing the rubber sleeve 5 from its initial position to the assembled position over the joint portion, the sleeve in its mounted position will have a residual prestressing to the effect that it is clamped tightly around the insulation and at a highest possible degree of sealing against the adjacent end or cutting surfaces of the rubber sheath 4 and 4A. A molded rubber sleeve may for example have a residual prestressing degree of 3-4 %. This results in a very strong and reliable encapsulation of the joint portion.

Possibly a sealant or an adhesive may be applied to the various surfaces during the construction of the protection and the insulation of the joint portion, before the sleeve 5 is mounted.

Additional details of the resulting joint structure appear from Fig. 4. Here are found again steel pipes 1 and 1A with the welding seam 10 as well as the corrosion protective layer 2, insulating layer 3 and sheath 4. Layer 12 in the joint portion is shown with an overlap with the corrosion layer on the adjacent pipe ends. Moreover, the insulating layer 13A,B is built up as will appear from the cross-section in Fig. 3. Outside the insulating layer 13A,B,C then lies the rubber sleeve 5 which has the same thickness as sheath 4. At the end or sectional surfaces at both sides of the joint portion there is shown a sealant or an adhesive 7 as mentioned above. This is preferably curable and may for example consist of polyurethane.The corresponding seams at the surface and around the periphery of the assembled pipeline may advantageously be covered withan asphalt composition, an adhesive tape or a rubber tape applied with a certain prestressing according to a similar principle as the sleeve 5. Such a rubber tape 9 consisting of an endless ring which beforehand has been mounted on the pipe ends before welding, contributes to a quick and safe joining procedure.

From the above it would appear that the manufactured pipe sections having corrosion protection and insulation as well as a prestressed rubber sleeve mounted beforehand, to a high degree make possible a comfortable and reliable joining at the building or working site such as a laying vessel for a subsea oil pipeline. The pipe sections may suitably be delivered from the manufacturing plant with a rubber sleeve on one end, in order that each joint portion has an accompanying sleeve.

However, there may also be thought of a modification to the effect that every second pipe section has been provided with two sleeves, i.e. one at either end, whereas every second or every intermediate pipe sections do not have any sleeve. As usual there may be applied a layer of concrete outside rubber sheath 4 and, moreover, a concrete layer may be applied over the joint portion outside the sleeve. Finally, it will be realized that in certain uses such pipelines do not require any heat insulation. Also when the pipeline is without an insulating layer, however, the joining method described here will be of much interest and involves the same advantages as described above with respect to insulated pipelines. In both cases it is essential that the inner metal or steel pipe shall have a reliable protection against corrosion and other stresses to which the structure is subjected during installation and particularly during long time operation under various influences.

Claims

1. Method of joining a corrosion protected pipeline, comprising a metal pipe (1) having a corrosion protective layer (2) and outside this possibly an insulating layer (3) as well as an outer sheath (4), preferably of rubber, wherein sections of the metal pipe (1, 1A) are welded together (10) at each joint portion, are then corrosion protected and possibly insulated, for example with PVC foam (13, 13A, 13B), characterized in that adjacent an end of the metal pipe (1) on the exterior of the outer sheath (4) there is mounted a rubber sleeve (5) under radial prestressing, that the rubber sleeve after welding of the metal pipe (1) to an adjacent pipe (1A) and application of a corrosion protective layer (12) and possibly an insulating layer (13, 13A, B) on the joint portion, is displaced longitudinally onto the joint portion and under radial elastic contraction is allowed to clamp tightly and with a residual prestressing about the joint portion.

2. Method according to claim 1, characterized in that the mounting of the rubber sleeve (5) adjacent an end of the metal pipe (1) is effected in connection with the application of the corrosion protective layer (2), possibly the insulating layer (3) and the outer sheath (4) along the length of the metal pipe (1) in a manufacturing plant, and that the displacement and the final mounting of the sleeve (5) over the joint portion is carried out at theworking site concerned, during laying of the pipeline, after welding (10), applying of corrosion protective layer (12) and possible insulating layer (13, 13A, B) on the joint portion.

3. Method according to claim 1 or 2, characterized in that there is applied a vacuum effect provided by a vacuum head (20) adapted to be applied around the rubber sleeve (5) in order to expand the same and to displace it by movement of the vacuum head (20) over the joint portion, whereafter the vacuum effect is released and the sleeve (5) contracts around the joint portion.

4. Method according to claim 3, characterized in that the vacuum effect (21) is applied with a shock-like pressure reduction.

5. Method according to claim 1 or 2, characterized in that before displacement of the rubber sleeve (5) there is injected a lubricant, for example polyurethane, between the sheath (4) and the sleeve.

6. Method according to claim 1, 2 or 5, characterized in that before and during dis placement of the rubber sleeve (5) there is supplied compressed air between the sheath (4) and the sleeve.

7. Method according to any one of claims 1 8, characterized in that there is employed a rubber sleeve (5) having a wall thickness being substantially equal to the thickness of the outer sheath (4), and preferably in its mounted position being adapted to lie with its outer surface flush with the outside of the sheath (4).

8. Method according to any one of claims 1-7, characterized in that a preferably curable sealing and adhesive agent (7) such as polyurethane, is applied to the insulating layer (13 A,B) and the sectional surfaces of the pipe insulation (3) and the sheath (4) during the joining.

9. Method according to any one of claims 1-8, characterized in that the seams between the mounted rubber sleeve (5) and the sheath (4) are covered with an annular rubber tape (9) which is mounted and maintained in position by a radial elastic prestressing in analogy with the sleeve.

10. Method according to any one of claims 1-9, characterized in that as a corrosion protective layer (12) on the joint portion there is applied a selfcuring or self-vulcanizing material which is cured or vulcanized at a comparatively low temperature.

11. Pipe section or length for corrosion protected pipeline and for use in the method according to any one of claims 1-10, comprising a metal pipe (1) with a corrosion protective layer (2) and outside this possibly an insulating layer (3) as well as an outer sheath (4), preferably of rubber, in which short end portions of the pipe for the purpose of joining is without any corrosion protective layer (2), possibly insulating layer (3) and sheath (4), characterized in that adjacent at least one end portion there is provided a rubber sleeve (5) which surrounds the outer sheath (4) with a radial prestressing force.